To ensure your photos are nice and sharp you need to understand how depth of field works. You might want a fuzzy background to concentrate a viewer’s attention on one part of the image such as a portrait or close up. This is called a shallow depth of field.
If you’re shooting a landscape you are likely to want the whole scene sharp and in focus from just in front of the camera all the way to the horizon. This is a wide or large depth of field. This video gives you a demonstration
Think of depth of field as a block of sharpness that you can change the size of and where you want to place it in your image. The main control for more or less depth of field is your aperture setting – BUT different focal length lenses have different amounts of DOF available. A short wide lens has loads of it where as a long lens has much less. And just to throw a spanner into the works the distance you are from your point of focus has an impact too.
I know it all sounds terribly complicated but please bear with us. We have a video explaining the different characteristics of focal lengths on our site at which demonstrate all this.